Color photographic silver halide materials are used to provide color images with the use of certain dye forming compounds that are usually in the various photosensitive silver halide layers of the materials. These dye forming compounds are conventionally known as "dye forming couplers" and are reactive with suitable oxidized forms of color developing agents used during photoprocessing to provide the desired dye images. Since most of such silver halide materials (such as color negative films and color papers) provide images based on what is known in the art as "subtractive color mixing", they typically include dye forming couplers that will provide cyan, yellow and magenta dyes in the appropriate photosensitive layers.
Pyrazolotriazoles have been known to be useful magenta dye forming couplers for some time, and various processes are known for preparing them, all of which usually include various chemical reactions taken in specific order. Such processes add functionality that defines the desired dye forming coupler early in the synthesis. These processes result in the lack of generality of the process and the need to make different intermediates for different dye forming coupler end products.
It is well known in the art [for example, U.S. Pat. No. 5,183,728 (Romanet et al), U.S. Pat. No. 5,457,210 (Kim et al) and U.S. Pat. No. 5,565,572 (Potenza et al)] that compounds defined by Formula IV below are known to be photographic dye forming couplers, as well as precursors to other photographic dye forming couplers.
It is known from EP 779,543 (Bose et al) that one common synthetic route to these types of compounds involves the high pressure catalytic reduction of a nitro aromatic compound (shown as Formula II below) using hydrogen to form an aromatic amine of Formula III, and then reaction of the aromatic amine with a compound of Formula IV under basic conditions. This is generally a two step process involving the isolation and handling of the aromatic amine of Formula III. ##STR1##
There are several disadvantages to such a two-step process. It includes increased cycle time due to increased handling requirements, increased air emissions if drying of the intermediate is required, and increased total volume of solvent needed. In addition, with this particular synthetic route, two different types of reaction vessels are needed. The catalytic hydrogenation of the first step requires specially designed high pressure equipment, while the displacement second reaction can be carried out in a standard reaction vessel. Additionally, this method requires the use of highly flammable hydrogen gas that presents a critical safety issue.
It is a desire in the industry to identify a chemical process that would transform aromatic nitro compounds of Formula II and the compounds of Formula IV into coupler precursors or couplers of Formula I in one step using one reaction vessel. It is also desired to accomplish this task with high chemical yield, high purity, short cycle time, low solvent usage, increased safety and minimal negative environmental impact.
One possible alternative to catalytic hydrogenation is a hydrogen transfer reaction [as described for example by Johnstone, et. al, Chem. Rev., 1985, 85, 129, Entistle, et. al, J. Chem. Soc., Perkin I, 1977, 443, and U.S. Pat. No. 5,041,605 (Huson et al)]. There are many possible hydrogen sources that can be used but each results in a different by-product.
Thus, there remains a need for an improved, single reaction medium synthesis of pyrazolotriazole dye forming coupler intermediates.